1. Field of the Invention:
The present invention relates to novel compositions of matter comprising a barium titanate powder dispersed in an organic matrix and suitable for use as absorbers of electromagnetic waves, in particular microwaves.
This invention also relates to a process for the preparation of finely divided barium titanate especially adapted for the production of such electromagnetic wave absorbers, and to the production of seals from the subject novel compositions, notably seals for microwave ovens.
2. Description of the Prior Art:
Absorbers of electromagnetic waves and, in particular, of microwaves are well known to this art and have been abundantly described in the literature.
The best known and most typically used absorbers are those based on ferro- or ferrimagnetic materials, such as, for example, the ferrites, which are used either in sintered form, or in the form of powders dispersed in organic resins (compare, e.g., U.S. Pat. Nos. 4,003,840, 4,023,174 and 4,414,339).
The use of metallic fabrics as microwave absorbers has also been described. In this case, very fine fibers of metals or alloys, optionally ferromagnetic, are used; they either may or may not be embedded in an organic polymer.
Certain patents (e.g., U.S. Pat. Nos. 4,200,701 and 4,281,072) also describe materials based exclusively on polymers, such as, for example, polypropylene foam, which are suitable for use in the absorption of microwaves.
More practically, in U.S. Pat. No. 4,027,384 microwave absorbers are described which comprise polymers filled with carbon or graphite, i.e., semiconducting fillers.
It too is known that a sintered ferroelectric material such as barium titanate has certain absorbent properties relative to electromagnetic waves, but it has been indicated that these absorbent properties disappear if the product is reduced to powder form. This would explain why absorbers filled with barium titanate have not to date found applications on an industrial scale.